Posts Tagged 'Cymothoid'

Isopod crustaceans exhibit a wide variety of morphologies and lifestyles. For instance, the common pill bug or woodlouse, found under any log in North America, is an isopod. These isopods, of the suborder Oniscidea, are the most terrestrially adapted of the crustaceans (unless you count insects, which you probably should). However, it is in aquatic environments that you see the true breadth of isopod diversity. I talked about two good examples in a previous post: Serolid isopods have flattened, trilobite-like bodies and scavenge on marine sediment; and Antarcturid isopods are narrow, with long forelimbs for catching prey from the water column. Other isopod suborders have developed parasitic lifestyles.

Many aquatic isopods are parasites that live either on the surface or inside their hosts. Some, the Epicarids for example, display morphological modifications characteristic of parasites; including reduction of appendages and sensory organs as well as a loss of rigid segmentation. Also, the mouthparts are sometimes specialized into a suction apparatus, complete with piercing stylets, used for extracting fluid from their hosts. These isopods parasitize copepods as larvae and then decapods as adults; living inside the carapace or gill chambers of crabs and shrimp. Other isopods parasitize fish, attaching to the body or gill chamber and feeding on the scales, flesh, or blood of the animal. Some of these isopods attack and kill fish in large swarms.

Parasitic isopods do some some fairly gristly stuff that is typical of parasites…

…but then there’s this… Oh, god… the horror…

I added LoL speak to make this a little less revolting. Alternate caption: 'Oh hai! Your tongue used to be here, but I eated it. Om-nom nom.'

Meet Cymothoa exigua, a Cymothoid isopod. Most Cymothids are exoparasites that feed on the flesh of fish. However this lifestyle has the disadvantages of exposing the isopod to predation and requiring it to migrate from fish to fish. C. exigua solves these problems by doing something disturbing.

Photo: Matthew Gilligan, Savannah State College, Savannah, GA (1989)

C. exigua parasitizes rose spotted snappers. It enters the fish through the gills and lodges itself in the buccal cavity at the back of the mouth. There it severs blood vessels leading to the fish’s tongue, causing the tongue to atrophy and degenerate. The isopod then uses its hook like pereopods to attach to the tongue nub, effectively and functionally replacing the snapper’s tongue. There it stays, feeding on blood, mucus, and stray pieces of whatever the fish is eating for the rest of its life.

Imagine being a rose spotted snapper, cruising around the comfortable waters of the gulf of California. One day this hard, spikey creature enters your mouth through your breathing apparatus, violently removes your tongue, and takes up residence. You have no arms or hands to reach into your mouth and remove it: So there it stays, drinking your blood and stealing your food, unmolested, …for ever…